Noise and vibrations may cause emotional unease and diseases and may make people easily tired. In modern society, due to changes in lifestyles, the daily travel range of people has markedly increased on average, and thus people often spend a relatively large amount of time in various means of transportation. Therefore, noise and vibrations in a means of transportation have a large effect on quality of life.
Manufacturers of means of transportation such as automobiles commonly use high-strength steels to ensure the safety of passengers and reduce the weight of vehicles in line with environmental regulations. However, high-strength steels commonly have a low degree of formability, and thus it remains difficult to use high-strength steels for manufacturing a means of transportation.
In general, materials for a means of transportation are required to have high strength and formability. Thus, in the related art, advanced high strength steels (AHSS) including martensite, bainite, or retained austenite, such as dual phase steel, bainite steel, or transformation induced plasticity steel, have been used. However, the formability of AHSS is inversely proportional to strength, and the vibration damping capacity of AHSS is low.
Vibration damping capacity refers to the property of a material that absorbs vibrations. In general, if a material is vibrated, the material absorbs vibration energy and dampens vibrations. This is known as the vibration damping capacity or vibration-proof properties of a material. The vibration damping capacity of a material may be evaluated by measuring the amount of energy that a material is able to absorb. In this regard, a method of measuring internal friction is widely used.
In general, the vibration damping capacity of metals is inversely proportional to the strength of the metals, and thus it is difficult to increase both the strength and vibration damping capacity of metals. FIG. 1 illustrates a relationship between specific damping capacity (SDC) and tensile strength (TS). Referring to FIG. 1, as tensile strength increases, vibration damping capacity (specific damping capacity, SDC) decreases.
Although the use of high-strength materials in a means of transportation has been increasingly required by enhanced safety and environmental regulations, it remains difficult to use existing high-strength steels for manufacturing a means of transportation.
Materials such as cast iron have a high degree of vibration damping capacity. However, such materials are not suitable for manufacturing a means of transportation because bodies or external panels of a means of transportation are formed of plate-shaped materials. In addition, although materials such as plastics, aluminum, or magnesium have a high degree of vibration damping capacity, the use of such materials increases manufacturing costs.